diff --git a/cozy/model/library.py b/cozy/model/library.py
index e25dcb8c..d377dece 100644
--- a/cozy/model/library.py
+++ b/cozy/model/library.py
@@ -93,10 +93,8 @@ def rebase_path(self, old_path: str, new_path: str):
         self.emit_event_main_thread("rebase-started")
 
         chapter_count = len(self.chapters)
-        progress = 0
-        for chapter in self.chapters:
+        for progress, chapter in enumerate(self.chapters, 1):
             if chapter.file.startswith(old_path):
-                progress += 1
                 chapter.file = chapter.file.replace(old_path, new_path)
                 self.emit_event_main_thread("rebase-progress", progress / chapter_count)
 
diff --git a/cozy/view_model/book_detail_view_model.py b/cozy/view_model/book_detail_view_model.py
index e3d2973a..4eb7e9c9 100644
--- a/cozy/view_model/book_detail_view_model.py
+++ b/cozy/view_model/book_detail_view_model.py
@@ -196,7 +196,7 @@ def _on_playback_speed_changed(self):
         self._notify("total_text")
 
     def _on_offline_cache_event(self, event, message):
-        if not self._book or self._book.id != message.id:
+        if not (message and self._book) or self._book.id != message.id:
             return
 
         if event in {"book-offline-removed", "book-offline"}: